Who is Lily and Nona Foster, Ruth's great-aunts from Housekeeping and what is their importance?

Ruth's great-aunts, Lily and Nona Foster, are reffered to as the two nervous elderly aunts. They always appear together, and for the most part, speak only to each other. They both have "light blue hair and black coats with shiny black beads in intricate patterns on the lapels". They look maternal with stout, matronly figures, but they are far from maternal and extremely awkward around children.